adapted to Kick Assembler, some documentation update
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@@ -1,76 +1,77 @@
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;; Pack a word using the simple compression scheme.
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;; This has to be the same implementation as in compress_text.c
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;; because we compress input lines of BASIC to do the tokenisation.
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;; This allows us to search through the compressed tokens directly
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;; using the compressed fragment of BASIC, and thus work out the
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;; token for a given piece of string.
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;; This also helps ensure that we have an implementation that is totally
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;; different to that of the original C64 BASIC, as well as likely
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;; saving a bit of space in the ROM, especially once we start implementing
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;; larger keyword vocabs for BASIC 7 or BASIC 10 compatibility, since the
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;; compression and decompression machinery is of fixed size.
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// Pack a word using the simple compression scheme.
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// This has to be the same implementation as in compress_text.c
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// because we compress input lines of BASIC to do the tokenisation.
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// This allows us to search through the compressed tokens directly
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// using the compressed fragment of BASIC, and thus work out the
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// token for a given piece of string.
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// This also helps ensure that we have an implementation that is totally
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// different to that of the original C64 BASIC, as well as likely
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// saving a bit of space in the ROM, especially once we start implementing
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// larger keyword vocabs for BASIC 7 or BASIC 10 compatibility, since the
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// compression and decompression machinery is of fixed size.
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pack_word:
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;; Inputs:
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;; X = offset of string to pack. Address is $0200 + X
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;; tokenise_work1 = number of bytes to pack
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;; tokenise_work2 = packed length of string
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// Inputs:
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// X = offset of string to pack. Address is $0200 + X
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// tokenise_work1 = number of bytes to pack
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// tokenise_work2 = packed length of string
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;; Outputs:
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;; Output is written to $0100 (bottom of stack).
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// Outputs:
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// Output is written to $0100 (bottom of stack).
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;; Memory modified:
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;; tokenise_work4 = temporary storage
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;; tokenise_work3 = flag for whether we have a nybl prepared or not.
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;; (This can also be checked on exit, to know whether the last byte
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;; is incomplete, which is important for searching for abbreviated
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;; key words.)
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// Memory modified:
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// tokenise_work4 = temporary storage
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// tokenise_work3 = flag for whether we have a nybl prepared or not.
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// (This can also be checked on exit, to know whether the last byte
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// is incomplete, which is important for searching for abbreviated
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// key words.)
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;; Make sure we have a sane request
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// Make sure we have a sane request
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lda tokenise_work1
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bne +
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bne !+
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sec
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rts
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*
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;; Initialise internal variables
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!:
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// Initialise internal variables
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lda #$00
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sta tokenise_work2
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sta tokenise_work3
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pack_char_loop:
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;; Get the next char
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// Get the next char
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lda $0200,x
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;; Work out what type of character we have, and thus
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;; how we need to pack it.
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// Work out what type of character we have, and thus
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// how we need to pack it.
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jsr get_packed_char_index
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cmp #$00
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bne not_exception_char
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;; Char is an exception char.
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;; We need to either finish the previous byte with $xF,
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;; Or if there is no existing nybl, then we need to output
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;; either $FE or $FF, depending on whether this is the last
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;; byte or not
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// Char is an exception char.
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// We need to either finish the previous byte with $xF,
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// Or if there is no existing nybl, then we need to output
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// either $FE or $FF, depending on whether this is the last
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// byte or not
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lda tokenise_work3
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bne have_nybl_before_exception_char
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;; No nybl exists before the exception char, so prefix with $FE or $FF
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;; based on whether we are at the end of the input string or not
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// No nybl exists before the exception char, so prefix with $FE or $FF
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// based on whether we are at the end of the input string or not
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inx
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lda tokenise_work1
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cmp #$01
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beq at_end
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lda #$FF
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.byte $2C
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at_end: LDA #$FE
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at_end:
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lda #$FE
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dex
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jsr write_unpacked_char
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;; Fall through
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// Fall through
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output_exception_byte:
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lda $0200,x
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@@ -78,18 +79,18 @@ output_exception_byte:
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jmp consider_next_char
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have_nybl_before_exception_char:
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;; Or existing byte with #$0F, and clear nybl flag
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// Or existing byte with #$0F, and clear nybl flag
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ldy tokenise_work2
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lda $0100,y
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ora #$0f
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sta $0100,y
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inc tokenise_work2
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;; FALL THROUGH
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// FALL THROUGH
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write_literal_and_terminate_if_required:
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;; Clear have nybl flag
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// Clear have nybl flag
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lda #$00
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sta tokenise_work3
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@@ -99,19 +100,19 @@ write_literal_and_terminate_if_required:
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jmp end_string_if_required
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end_string_if_required:
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;; Check if X points to last char of string to be packed
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// Check if X points to last char of string to be packed
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inx
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lda tokenise_work1
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cmp #$01
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beq +
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beq !+
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dex
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jmp consider_next_char
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*
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!:
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dex
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;; Fall through
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// Fall through
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end_string:
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;; Write end of string sequence if required
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// Write end of string sequence if required
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lda #$00
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jsr write_unpacked_char
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rts
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@@ -124,53 +125,53 @@ write_unpacked_char:
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rts
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not_exception_char:
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;; It wasn't an exception char, so write the symbol out
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// It wasn't an exception char, so write the symbol out
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cmp #$10
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bcs whole_byte_symbol
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;; Nybl encoded value: Put in upper half or lower half of a byte?
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// Nybl encoded value: Put in upper half or lower half of a byte?
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ldy tokenise_work3
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bne store_low_nybl
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;; Store in high nybl -- so shift it into the hi nybl
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// Store in high nybl -- so shift it into the hi nybl
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asl
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asl
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asl
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asl
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ldy tokenise_work2
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sta $0100,y
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bne stored_nybl ; Must be taken, as A cannot be $00
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bne stored_nybl // Must be taken, as A cannot be $00
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store_low_nybl:
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;; Low nybl gets added to high nybl already stored in the byte
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// Low nybl gets added to high nybl already stored in the byte
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ldy tokenise_work2
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ora $0100,y
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sta $0100,y
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stored_nybl:
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;; Now toggle the nybl flag
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// Now toggle the nybl flag
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lda tokenise_work3
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eor #$ff
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sta tokenise_work3
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;; And advance the offset if we filled this byte up
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bne consider_next_char ; Taken if byte has a nybl free, i.e., don't advance pointer while half byte remains free
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// And advance the offset if we filled this byte up
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bne consider_next_char // Taken if byte has a nybl free, i.e., don't advance pointer while half byte remains free
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;; Count the filled up byte
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// Count the filled up byte
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inc tokenise_work2
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;; Add termination byte if required
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;; (This re-writes the same byte again, which we don't care about)
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// Add termination byte if required
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// (This re-writes the same byte again, which we don't care about)
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jmp end_string_if_required
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whole_byte_symbol:
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;; It's a $Fx symbol.
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;; But if we have a nybl to flush, then we handle it like
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;; a full exception character
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// It's a $Fx symbol.
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// But if we have a nybl to flush, then we handle it like
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// a full exception character
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ldy tokenise_work3
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beq nothing_to_flush
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;; Set low nybl to $F to mark next byte as literal
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// Set low nybl to $F to mark next byte as literal
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ldy tokenise_work2
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lda $0100,y
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ora #$0f
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@@ -180,30 +181,30 @@ whole_byte_symbol:
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jmp write_literal_and_terminate_if_required
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nothing_to_flush:
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;; Write the symbol as it is, or the literal
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;; if it has been passed to us via fall-through
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// Write the symbol as it is, or the literal
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// if it has been passed to us via fall-through
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jsr write_unpacked_char
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jmp end_string_if_required
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consider_next_char:
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;; Pack next char
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// Pack next char
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inx
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dec tokenise_work1
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beq +
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beq !+
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jmp pack_char_loop
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*
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;; Add 1 to length if nybl waiting to be flushed
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;; (but leave flag set so the caller knows if the
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;; bottom nybl might be different if the string were
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;; longer).
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!:
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// Add 1 to length if nybl waiting to be flushed
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// (but leave flag set so the caller knows if the
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// bottom nybl might be different if the string were
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// longer).
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lda tokenise_work3
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beq +
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beq !+
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inc tokenise_work2
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rts
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*
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;; Last byte was full, so we need at $00 on the end
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;; (unless a $FE token was written 2 bytes ago)
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!:
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// Last byte was full, so we need at $00 on the end
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// (unless a $FE token was written 2 bytes ago)
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ldy tokenise_work2
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iny
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lda #$00
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@@ -213,21 +214,21 @@ consider_next_char:
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rts
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get_packed_char_index:
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;; Find char in A in the packed char list, and return
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;; $1 - $E, $F1 - $FD if the charactar is abbreviable,
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;; or else return $00 if the character has to be stored literally.
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// Find char in A in the packed char list, and return
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// $1 - $E, $F1 - $FD if the charactar is abbreviable,
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// or else return $00 if the character has to be stored literally.
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;; Y register and A are modified, as are processor flags.
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// Y register and A are modified, as are processor flags.
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ldy #$00
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find_char_loop:
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cmp packed_message_chars,y
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bne not_a_match
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enumerate:
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;; Is it a nybl abbreviable char?
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// Is it a nybl abbreviable char?
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cpy #14
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bcs not_nybl_char
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;; Yes, so add 1 and return it
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// Yes, so add 1 and return it
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iny
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tya
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rts
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@@ -235,9 +236,9 @@ enumerate:
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not_nybl_char:
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cpy #27
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bcs not_a_match
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;; It's a $Fx character.
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;; Since the lowest index is $E, and it should be encoded as $F1
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;; we need to add $E3
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// It's a $Fx character.
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// Since the lowest index is $E, and it should be encoded as $F1
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// we need to add $E3
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tya
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clc
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adc #$E3
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@@ -245,10 +246,10 @@ not_nybl_char:
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not_a_match:
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iny
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;; Loop until we find it, or we discover it isn't
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;; a character with a special encoding
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// Loop until we find it, or we discover it isn't
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// a character with a special encoding
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cpy #27
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bne find_char_loop
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;; Not a char that we can pack, so return 0
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// Not a char that we can pack, so return 0
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lda #$00
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rts
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